1. Field
The following description relates to a wireless signal receiving apparatus, and more particularly, to a parallel automatic frequency offset estimation apparatus and method in an early stage a frequency offset by calculating frequency offsets of a received signal in parallel.
2. Description of the Related Art
A wireless transmission data frame suggested by ISO/IEC (International Standard Organization/International Electrotechnical Commission) 24730-2 or 18185-5 type B is composed of a preamble section 100 and a payload section 102 as shown in FIG. 1. The preamble section 100 is used for an initial synchronization of a wireless signal receiver, and the payload section 102 contains information to be transmitted.
In the frame described above, channel estimation is performed in the preamble section before the payload in order to assist in stable verification of payload data. However, in acquisition of the frequency used for the channel estimation, it becomes more difficult to acquire a frequency when the size of preamble is short. To overcome such drawbacks, a multi-stage channel estimation method and apparatus has been disclosed.
In the multi-stage channel estimation method and apparatus, a channel estimation unit performs channel estimation for one-bit sections 104 and 106 within a preamble section and calculates a first channel estimation value for a wireless path. Then, the channel estimation unit adjusts a frequency and a phase difference using an automatic frequency controller and a digital-analog converter (DAC) in order to correct a frequency offset and a phase difference value which are obtained through the channel estimation. A compensation unit controls a frequency control device such as variable crystal oscillator using the corrected values to compensate for distortion of the wireless transmission data frame.
Subsequently, the channel estimation unit performs channel estimation for the next two-bit sections 108 and 110 within the preamble section, as shown in FIG. 1, and obtains a second channel estimation value while retaining the first channel estimation value. The channel estimation unit adjusts a frequency and a phase difference using the automatic frequency controller and the DAC in order to correct a frequency offset and a phase difference value which are obtained through the channel estimation. At this time, the channel estimation unit adds together the first channel estimation value and the second channel estimation value and corrects the result of the addition. The compensation unit controls the frequency control device, which may be embodied by a variable crystal oscillator or the like, using the corrected value to compensate for the distortion of the data frame secondarily. Then, the channel estimation unit performs channel estimation for the next one-bit sections 112 and 114 within the preamble section to obtain a third channel estimation value while retaining the first and second channel estimation values. The channel estimation unit adjusts a frequency and a phase difference using the automatic frequency controller and the DAC in order to correct a frequency offset and a phase difference value which are obtained through the channel estimation.
Afterwards, the channel estimation unit adds the third channel estimation value to the first and second channel estimation values and corrects the result of the addition. The compensation unit controls the frequency control device, which may be embodied by a variable crystal oscillator or the like, using the corrected value to finally compensate for the distortion of the wireless transmission data frame.
In the multi-stage channel estimation method and apparatus described above, a particular section is divided into several parts and an error is calculated for each part in order to obtain a frequency offset, resulting in complexity in configuration. Also, the frequency offset acquisition is performed in stages, and thus time delay is caused. In addition, since two types of sections (one-bit sections and two-bit sections) are used to acquire a frequency offset at initial time, bits other than those belonging to two sections cannot be utilized.